The field of the invention is Chemistry, carbon compounds of acyclic ketones and the invention is particularly concerned with a process for the selective manufacture of acetone by catalytic oxidative decarbonylation of isobutyraldehyde.
Isobutyraldehyde, which is obtained in very large amounts as an unavoidable by-product in the manufacture of n-butylraldehyde from propylene by the oxo synthesis, has hitherto been used almost exclusively only in power stations, for its calorific value.
The state of the art of isobutyraldehyde manufacture by the oxo process may be ascertained by reference to the "Kirk-Othmer Encyclopedia of Chemical Technology", Second Edition, Volume 14 (1967), pages 373-390, particularly pages 380 and 381 where it is disclosed in FIG. 2 and the text that when propylene is the olefin feed, isobutyraldehyde is a less desirable product. The state of the art of isobutyraldehyde conversion to acetone may be ascertained by reference to U.S. Pat. Nos. 3,804,902; 3,855,304 and 4,000,199; the disclosures of which are incorporated herein.
In the process disclosed in U.S. Pat. Nos. 3,804,902 and 3,855,304 isobutyraldehyde is oxidized to acetone in the gas phase with oxygen, on a catalyst consisting of manganese oxide and optionally an alkali metal oxide on activated aluminum oxide support. However, with an isobutyraldehyde conversion of 98 percent, the yield of acetone is still only 83 mole percent.
A substantially better selectivity is shown by the process disclosed in U.S. Pat. No. 4,000,199 whic has the same assignee as the present invention. In the process of U.S. Pat. No. 4,000,199 isobutyraldehyde is oxidized in the gas phase, on a catalyst consisting of copper II oxide with and without an inert support. The best selectivity which can be achieved, as disclosed in Example 6, is 96 mol percent and this is achieved on a catalyst with zinc oxide as the support. The isobutyraldehyde conversion is still only 90.5%.
U.S. Pat. No. 4,000,199 discloses in Column 3, line 35 the use of graphite as "an auxiliary tabletting agent" or mold lubricant but the concentration of graphite in the total catalyst is usually less than 2.5 weight percent.
Since as complete as possible an isobutyraldehyde conversion is necessary for economical commercial production of acetone, the isobutyraldehyde conversions and acetone yields achieved by the process of U.S. Pat. No. 4,000,199 which are in themselves already very good, are still not satisfactory for commercial production. In addition to the high conversion, a high selectivity, in particular, is also of great importance for the commercial profitability of a process of this type.
It is known that the throughput over the catalyst (that is the amount of isobutyraldehyde fed in per unit time) must be matched with the capability of removing the heat of reaction liberated, in order to avoid too steep a temperature profile with selectivity reducing high peak temperatures. A reduction of the total combustion permits a correspondingly higher throughput over the catalyst and thus a higher space/time yield of acetone. However, the space/time yield, that is to say the amount of product obtainable per catalyst volume and per unit time, is always highly important for a large-scale industrial process. In the case of total combustion of isobutyraldehyde, about five times more heat is liberated than in the case of partial oxidation of isobutyraldehyde to acetone. Even if only 4 mol percent of isobutyraldehyde undergoes total combustion in the process, to give not acetone but carbon dioxide and water, about one-fifth of the heat to be removed during the process can be attributed to this 4 mol percent of isobutyraldehyde which has undergone total combustion. Even small improvements in the activity and the selectivity therefore represent a considerable advance over the prior art.